1R24GM124135. Community Crystallization Resource for Biological Macromolecules Administrative Supplemental Support Request to purchase a Rock Imager 54 Imager (27 plate capacity) Project Abstract Macromolecular X-ray crystallography is one of the predominant methods used in structural biology, accounting for ~90% of solved structures in the Protein Data Bank, the primary repository and public database for making three-dimensional structures of biomolecules available to researchers in all fields. To do crystallography, we need crystals. Finding conditions in which a macromolecule will crystallize remains one of the most challenging steps in this process, and the one we have focused on solving at the High-Throughput Crystallization Screening Center (HTCSC) at Hauptman-Woodward Medical Research Institute (HWI). The HTCSC is a community resource that provides crystallization experiment set-up and imaging of a uniquely designed set of 1,536 crystallization conditions. Information about macromolecular crystallization is collected in a rapid and efficient manner, so that structural investigations for the entire user community can rapidly progress. The HTCSC has a robust imaging schedule that allows for immediate identification of positive crystallization outcomes. We have experienced an unanticipated increase in the number of experiments being requested by users for low temperature incubation and imaging, and this revision application seeks funds to address this unanticipated need through purchase of a Rock Imager 54 (with 27 plate capacity).